The goal of this research is the characterization of the biological role of the testis and sperm specific histone binding protein NASP (nuclear autoantigenic sperm protein) during spermatogenesis. Our hypothesis is that a histone-binding protein could function to bind and transport testicular histone from the cytoplasm into the nucleus during the two meiotic cell divisions after DNA replication has finished. By transporting testicular histone variants into the nucleus, such as histone-binding protein would participate in chromatin and nucelosome reorganization. NASP is hypothesized to be such a histone-binding protein based on its testis specificity its nuclear translocation signal, its similarity to the Xenopus histone binding protein N1/N2, and its conserved histone binding domains. Specifically, we are asking what role NASP plays in the movement, transport and transfer of testis specific histones, transition proteins or protamines from the cytoplasm to the nucleus and to the DNA of the spermatocyte or spermatid. Therefore, the Specific Aims of this proposal are to determine: 1) The specific binding and affinity of testicular histones, transition proteins, and protamines as well as somatic histones for NASP. 2) Whether NASP actually transports bound testicular and/or somatic histones into the mammalian cell nucleus. 3) Whether NASP will transfer its bound histones to DNA as has been demonstrated for Xenopus histone binding protein N1/N2. 4) The sequence of mouse NASP and its genomic organization in preparation for stage specific and gene targeting studies in the mouse. 5) Whether the synthesis of NASP during spermatogenesis in the mouse is coordinated with testicular histone synthesis, transition protein synthesis, protamine synthesis or all three of these.